A system for imaging a subject is provided. The system includes a radiation source, a radiation detector, and a controller. The radiation source is operative to transmit electromagnetic rays through the subject. The radiation detector is operative to receive the electromagnetic rays after having passed through the subject so as to generate a plurality of projections of the subject. The controller is operative to display one or more selectively adjustable markers that define an image stack. The controller is further operative to reconstruct one or more images within the image stack based at least in part on the plurality of projections. Reconstruction of the one or more images is on demand.